The present invention relates to a plastic conveyor belt of the type which in the belt transport course thereof undergoes course turns around short radii and, more particularly, to a plastic transport belt in which a unitarily structured module having inner section, central section and outer section parts is employed as the successive link members of which the belt is comprised.
Plastic conveyor belts are becoming more widely used for a number of reasons including the advantage offered by the convenience of molding of belt components as well as simplified fabrication operations associated with such as compared to metal belts. Also in some applications such as in food industry environments, plastic is less susceptible to creating contamination problems than many of the other materials of which belts are made.
While plastic belts are attractive and effective in many applications, they become more subject to failure possibility due to loading forces acting thereon when used on spiral conveyors or in conveyor systems where the belt in its load conveying travel course transits turns. In these turns, the part of the belt at the side to which the travel course turns (inner side) longitudinally shortens or collapses, whereas, the belt part at the side remote from the inner side (outer side), elongates longitudinally or expands.
In this turn travel, a link member component at the inner side is positively driven at its inner edge by, e.g., a rotary capstan and little difficulty attends driven movement of the inner side component. On the other hand, the further removed a link member component is from the said inner edge and particularly at the outer side of the belt, the more difficult it is drive the outer side through the turn.
Such difficulty arises because drive to an outer section component must be transferred thereto from an inner section component. Where a center section component or link such as that shown at 21 in FIG. 9 of pending Ser. No. 07/656,853 is used to intervene the inner and outer section components, drive must transfer through same as well. The disclosure of the said and soon to be patented Ser. No. 07/656,853 is incorporated herein by reference.
In the transfer of drive, large shear and bending moment loadings act on a connecting rod passing through these components. Bending moment effect on a plastic rod is especially severe in the central length part of the rod. These loadings are significant too because tension must be maintained on the belt to tighten the belt inner edge against the capstan.
Commonly, the plastic material components providing the inner and outer sections of what, in effect, constitutes a complete belt transverse link member, will be plural in number. Where these plural components abut one another as seen, e.g., in the above noted pending application FIG. 8, belt deflection loading compounds shear loadings on the rod especially at the central length part thereof. The more the number of individual parts which make up the link member, the more rod flexure will occur and to a degree that can be detrimental to continued rod integrity.
With prior plastic belts including those disclosed in Ser. No. 07/656,853, shear and bending moment loadings can become so severe that rod failure occurs. Also the forces acting on the belt components during a turn can in some cases cause bearing failure in the components making up the inner and outer belt sections.
Accordingly, it is desirable that a belt construction especially applicable to plastic transport belts be provided which reduces shear and bending moment problems associated with passage of the belt through turns.